Let me see if I can help the lovely Amy out of the corner.
Treating scale insects on ferns is tricky because many ferns are particularly sensitive to handling and to any chemicals, including soap and alcohol. In addition, many ferns produce spores that look a lot like brown scale.
If you have a Boston fern, then I suggest cutting off all of the folige at the soil line - a real crewcut. Discard all the infested foliage and drench the soil with Merit or Marathon if you can find it. Otherwise, don't worry about it. New growth will soon emerge as long as the roots are healthy.
If you have a maidenhair fern, it is too fragile to treat so write it off on your tax return - due in a month, BTW.
For most other ferns decide how valuable it is to you. If it doesn't pass the "I must save this
plant" test, then discard it.
If you have any ferns left at this point, then its time for a drink - rubbing alcohol diluted in water at a 1:8 ratio with a dash of liquid soap. After drinking that, you will be willing to discard all of your
plants!
Just kidding. Spray that concoction on all leaf and stem surfaces of your infested ferns until they are dripping wet. Complete coverage is essential to success because the juvenile scales are virtually invisible and if you miss a few, they will grow up and show up as adults in a copuple of weeks.
A note of caution: Both soap (especially Safer's) and alcohol have a drying effect and that is not good for ferns. So you are taking a chance with this dilute spray, but then what alternative do you have?
Good luck!